This invention has the aim of a method for treating industrial residual sludges.
More specifically, and always with the possibility of admitting other similar applications, the invention refers to a method for treating the sludge which comes from the industrial spray-gun painting procedure.
As is well know, in the industrial spray-gun painting of fabricated steel items, and especially in the painting of large-sized parts, such as the bodywork of cars, steel furniture, etc., a water curtain for protection is foreseen at the back wall of the corresponding painting cabin. This curtain catches the flying particles of paint, drives them down, thus preventing them accumulating on the mentioned wall, or, bouncing back to the worker and thus harming him. In this process, thus, a suspension of paint particles in water is continuously obtained as residue, with the corresponding solvent. This mixture is picked up in decanting trays in which the water is separated, the resulting mass being the so-called paint sludge, which contains an appreciable proportion of thermosetting resins, as well as pigments and mineral fillers.
If it is taken into account that, in general terms, up to fifty percent of the paint applied by spray-gun is caught and driven down by the water curtain, it is easy to imagine the enormous quantity of painting sludge produced in the industry. As is logical, this sludge must be removed. For this, the most generally used method consists of discharging it into large waterproofed concrete tanks or containers so as to prevent the filtration of the liquid components, which are later transported to determined removal points. As is logical, this elimination is relatively expensive; at present it is calculated at nine pesetas per kilogram, which obviously represents a direct expense for the industry; and moreover it brings about social costs which, although they are difficult to quantify, turn out less serious and real, given that the use of the container waste areas is forever affected, both for agriculture and for construction.
This invention aims precisely at a method which allows the recuperation of the solid part of the mentioned sludge, with view to a future practical use, by eliminating the liquid components--water and solvents--present in the sludge. In this way, the social problems and costs which are typical of the classical sludge elimination system mentioned above are solved completely, and the purely economic costs of this elimination are reduced appreciably: they are compensated to a large extent or even completely by the value of the solid components which are recuperated and used for later applications.